CEREAL PESTS—INSECTS AND FUNGI.

Otago Witness, Issue 3331, 16 January 1918, Page 8

CEREAL PESTS—INSECTS AND FUNGI.

The fact- that rust and plant lice (aphides) are more or less prevalent this season in the wheat area of Canterbury gives room for thought. The Ellesmere and Southbridge districts, it is reported, are adversely affected, while there is some evidence nearer home —in the Waimate district—that cereals (have not escaped infection. As is well known, there are numerous insect and fungoid pests which attack cereal plants, their ravages depending to a great extent upon the number of the enemy, the vigour of the plant, and the climatic conditions prevailing, at the present time, as well as during the preceding seasons. In any consideration of these menacing pests, it must not be forgotten that all members of the natural order —Graminefe —all grasses and cereals —are liable to suffer from rust or insect attack, so that although precautions may be taken, such as the using of seed from clean crops, etc., yet the vagrant grasses by the waysides and in. the hedgerows may all act as hosts, which may serve to support the pest. It is generally considered, too, that corn crops," grown on damp low-lying, badlv drained land, indifferently tilled, suffer most from fungi or insect pests, and those grown on open, elevated lands less in this" respect, the moist atmosphere being favourable to the development of the fungus spores. The development in the Canterbury province was deeded of sufficient 'import as to entail inspection by Dr A. H. Cockayne, biologist to the

Department of Agriculture. His report has been forwarded by the Director of Fields Division of the Agricultural Department to Mr A. Macpherson, Fields Supervisor of the South Island, and draws attention to, among other things, the conditions prevailing climatically since sowing time. The rainfall during the early period of growth was low, but extremely well distributed. As the water content waa low in the lower levels of the soil, in consequence of the two previous seasons' drought, the cereal crops became extremely surface-rooted, due to the small falls of rain which occured fairly regularly. Since the spring the rainfall has been small, and, in fact, at Southbridge, the present 12 months' rainfall is less than the -preceding 12 months. These conditions appear to have favoured an excessive development of corn aphis (aphis graminis). This insect is always present in fair numbers, but is kept in check by the seven spot ladybird. This year it the ladybird beetle must have been later than usual in appearing in sufficient numbers to keep the aphis in check, and, in consequence, this has increased enormously, and sapped the vitality of many «of the cereal crops. During my visit it was noticeable that in crops that had been very badly infested, but were now more or less free, ladybirds were present in large numbers. In crops where the aphis was still abundant, very few ladybirds could be seen. The presence of aphis in large quantities, even if the beetle were comparatively absent, would not been so particularly sferious had the cereal plants been deeply rooted, and not so surface-rooted as they are. The result has been that as soon as the plants lost vigour through the drying of the upper surface of the soil, the toll levied by the aphis was too severe for their proper development. Again, many of the crops (and this refers especially to Dun oats) have become very badly infested with rust; in fact, never before in my experience, except with regard' to white oats in certain parts of the North Island, have I seen such badly rusted crops while yet in the flag state. As far as I could see, the main damage was caused by corn aphis, against which there are no practical methods of control, nor are any methods of control necessary normal years when the ladybirds are present in their usual numbers. The actual damage caused by aphis is greatly intensified by the surface-rooted development of many of the crops and their inability to secure sufficient water for their increased requirements, due to the drain on them through aphis attacks. The extreme prevalence of rrist may or may not have been induced by the condition caused by aphis, but it is a significant fact that crops badly affected by aphis are now falling ready victims to rust. So far as future treatment to avoid a recurrence of is concerned, there is little of a practical nature that can be suggested. I consider that on many soils some system of green manuring should be adopted, as this should have a great effect on the better conservation and distribution of the soil moisture. Nature is at hand to help the farmer. Some of the worst foes of cropdestroying insects-are other insects, ""and these latter should be encouraged. Ladybirds devour all kinds of plant lice (aphides); therefore never kill a ladybird. Insectivorous birds should be encouraged, or at least they should not be ruthlessly destroyed. It is one object of the cultivator's skill, that whilst he is growing millions of wheat or turnip plants on a small area which would, in a natural state, be diversely clothed in vegetation, yet he must prevent or check a corresponding increase in the pests which infest those crops.